The present invention relates to the defoliation of crop plants. In preferred forms, the present invention is embodied in compositions and processes whereby crop plants (e.g., cotton) may be defoliated prior to harvest and/or to compositions which effectively prevent regrowth of defoliated crop plants.
Cotton is the most widely used textile fiber and is grown around the world. The cotton plant (Gossypium hirsutum) is a perennial plant of tropical origins that is cultivated in an annual manner in temperate regions.
The cotton plant continually produces fruit (bolls) starting at the seven to nine leaf stage through the end of the season. Generally, the bolls produced in the early part of the growing season obtain a larger size by harvest than the bolls produced in the last part of the growing season. The bolls produced in the first part of the season will open several days or weeks before the bolls produced in the last part of the season. However, once open, the cotton bolls begin to lose fiber quality due to the continued exposure to weather. For this reason, it benefits the cotton grower to begin harvesting before the plants are completely mature.
When cotton plants are mechanically harvested while green leaves remain on the plant, a green stain will often be visibly present on the cotton fiber during the harvesting process. This green stain reduces the value of the fiber at market. For this reason, a defoliation agent is often applied to the cotton plants before they are mechanically harvested. Although defoliation of cotton plants has been practiced in the past, there is still a need for improvement.
Broadly, the present invention relates to the discovery that the concurrent or sequential application of a plant growth regulator (preferably, an auxin transport inhibitor) and a defoliation agent (preferably, an ethylene response or ethylene-type response inducing agent) synergistically improve defoliation of crop plants and/or will minimize (if not prevent entirely) plant regrowth following defoliation. Preferably, the auxin transport inhibitor is a semicarbazone compound and the ethylene response or ethylene-type response agent is a phosphonic acid derivative. Most preferably, the semicarbazone compound is diflufenzopyr and the phosphonic acid derivative is ethephon (i.e., ethephon (2-chloroethyl) phosphonic acid).
Other aspects and advantages of the present invention will become more clear after careful consideration is given to the following detailed description of the preferred exemplary embodiments thereof.
The preferred auxin transport inhibitors that may be employed in the practice of the present invention include substituted semicarbazones and related compounds, such as thiosemicarcarbazones and isothiosemicarbzones and salts thereof, as described more fully in U.S. Pat. Nos. 5,098,462 and 5,098,466 (the entire content of each U.S. patent being expressly incorporated hereinto by reference). These compounds may be synthesized by reacting a carbonyl compound and a semicarbazide or thiosemicarbazide together at room temperature in the presence of an alcohol solvent, such as methanol or ethanol and with or without an acid catalyst to give the semicarbazones that may be employed in the practice of the present invention. The most preferred semicarbazone employed in the practice of this invention is diflufenzopyr.
The preferred ethylene response or ethylene-type response inducing agent is a compound of the following formula: 
wherein:
R1 is haloethyl, and R2 and R3 are selected from (1) a chlorine atom and a hydroxy group, (2) the group xe2x80x94OR4 and the group xe2x80x94Oxe2x80x94CH2R4 wherein each R4 is one member of the group of unsubstituted aryl, substituted aryl and a heterocyclic group, (3) the group xe2x80x94OR4 and the group xe2x80x94Oxe2x80x94CH2R4 wherein each R4 is a different member of the group of hydrogen, unsubstituted alkyl, substituted alkyl, unsubstituted cycloalkyl, substituted cycloalkyl, unsubstituted aryl, substituted aryl, a heterocyclic group, alkene and alkyne, provided that when one R4 is selected from unsubstituted alkyl, substituted alkyl, alkene and alkyne, the other R4 is selected from unsubstituted aryl, substituted aryl and a heterocyclic group, (4) together R2 and R3 represent the group: 
where R5 and R6 are each connected to the phosphorous atom by a separate single bond, and where one of R5 and R6 is xe2x80x94Oxe2x80x94 and the other is selected from the group of xe2x80x94Oxe2x80x94, xe2x80x94OCH2, xe2x80x94COxe2x80x94Oxe2x80x94 and xe2x80x94CONH, and R7 represents a cyclic group selected from benzene, substituted benzene, a heterocyclic ring and a substituted heterocyclic ring, (5) one of R2 and R3 is xe2x80x94OR8 and the other is: 
wherein each R8 is the same or different and is selected from hydrogen, unsubstituted alkyl, substituted alkyl, unsubstituted aryl, substituted aryl and a heterocyclic group, and wherein R1 is as defined above.
Suitable ethylene response and ethylene-type response inducing agents within the definition above are described in U.S. Pat. Nos. 3,879,188, 4,240,819, 4,352,869, 4,374,661, 4,401,454 and 5,123,951, the entire content of each such patent being incorporated expressly hereinto by reference. The most preferred ethylene inducing agent is 2-chloroethyl-phosphonic acid colloquially known as ethephon as well as its immediate derivatives.
Specific phosphonic acid derivative compounds usable in the practice of the present invention include the bis(acid chloride) or 2-chloroethylphosphonic acid, the pyrocatechol cyclic ester of 2-chloroethylphosphonic acid, the 4-chloropyrocatechol cyclic ester of 2-chloroethylphosphonic acid, the mixed ethyl and 2-hydroxyphenyl diester of 2-chloroethyl-phosphonic acid, the mixed butyl and 2-hydroxyphenyl diester of 2-chloroethyl-phosphonic acid, the 2-chloroethyl monoester of 2-chloroethylphosphnic acid, 2-bromoethylphosphonic acid, the bis(phenyl)ester of 2-chloroethylphosphonic acid, the tetrachloropyrocatechol cyclic ester of 2-chloroethylphosphonic acid, 2-iodoethylphosphoic acid, the saligen cyclic ester of 2-chloroethylphosphonic acid, salicyclic acid cyclic ester of 2-chloroethylphosphonic acid, the ethyl monoester of 2-bromoethylphosphonic acid, the butyl monoester of 2-iodoethylphosphonic acid, the 3-hydroxyphenyl monoester of 2-chloroethylphosphonic acid (which exists in polymeric form), the bis(2-oxo-prrolidinylmethyl) ester of 2-chloroethylphosphonic acid, the o-hydroxyphenyl monoester of 2-chloroethylphosphonic acid, the mixed isopropyi and 2-hydroxyphenyl diester of 2-chloroethylphosphonic acid, 2-fluoroethylphosphonic acid, the mixed octyl and 2-hydroxyphenyl diester of 2-chloroethylphosphonic acid, the mixed hexadecyl and 2-hydroxyphenyl diester of 2-chloroethylphosphonic acid, the mixed tridecyl and 2-hydroxyphenyl diester of 2-chloroethylphosphonic acid, the anhydride of 2-chloroethylphosphonic acid, 2-chloroethylphosphonic acid, the mixed butyl and 2-hydroxyphenyl diester of 2-chloroethylphosphonic acid, and the 2-bromoethyl monoester of 2-bromoethylphosphonic acid.
Other useful phosphonic acid derivative compounds within the above formula include salicyclic acid cyclic ester of phosphonamidic acid, the mixed phenyl and 2-hydroxyphenyl diester of 2-chloroethylphosphonic acid, 2-chloroethyldichlorophosphine, the bis (pentachlorophenyl) ester of 2-chloroethylphosphonic acid; 2-chloropropylphosphonic acid, 2-phenylthioethylphosphonic acid, the 2,3-pyridinedio cyclic ester of 2-chloroethylphosphonic acid, 2-chloroethylthiophosphonic acid, (2-bromo, 2-fluoro and 2-iodo) and 2-chloroethyl-2,3-dibromo4-hydroxy-2-butenyl ester polymer. Salts of the phosphonic derivatives of this invention may be used. Examples of such salts include the sodium, aluminum, zinc, potassium and lithium salts.
The semicarbazone is applied to the locus of growing crop plants at rates ranging between 0.005 to about 0.09, and more preferably between about 0.01 to 0.05, pounds of active ingredient per acre (lb. ai/A). The ethylene response or ethylene-type response inducting agent, on the other hand, is most preferably applied to the locus of the plant in an amount between about 0.25 to about 2.5 lb. ai/A, more preferably in an amount between about 0.5 to about 2.0 lb ai/A. The active ingredients may be applied concurrently to the plant (e.g. as part of a tank mixture of ingredients), or may be applied sequentially. If applied sequentially, it is most preferred that the semicarbazone compound be applied to the locus of the growing plant first, followed within at least about 3 to about 21 days of the semicarbazone compound application, by the application of the ethylene response or ethylene-type response inducing agent. When applied sequentially, then the respective amounts of active ingredient applied should be within the ranges noted above.
The active ingredients may be applied either collectively or sequentially in the form of dusts, granules, solutions, emulsions, wettable powders, flowables and suspensions. Application of a compound as an active ingredient is made according to conventional procedure to the locus of the plant in need of the same using the appropriate amount of the compound per acre as will be described below. According to the present invention the application of the compound to the xe2x80x9clocusxe2x80x9d of the plant includes application to the plant or parts of the plant or the soil in which the plant is growing.
The active ingredients be applied to above ground portions of the plants. The application of liquid and particulate solid compounds and/or compositions to above ground portions of plants may be carried out by conventional methods, for example, boom and hand application, including sprayers or dusters. The compounds and/ or compositions may be applied aerially as a spray, if desired. The active ingredients employed in the practice of the present invention are most preferably used in the form of aqueous solutions. The solutions may be applied in a conventional manner, for example, by spraying, atomizing or watering the locus of the plant.
The active ingredients may also be applied in conjunction with other ingredients or adjuvants commonly employed in the art. Examples of such ingredients include drift control agents, defoaming agents, preservatives, surfactants, fertilizers, phytotoxicants, herbicides, pesticides, insecticides, fungicides, wetting agents, adherents, nematocides, bactericides, trace elements, synergists, antidotes, mixtures thereof and other such adjuvants well known in the plant growth regulating art.